Fix 8 bugs found in code review

- auth/login.py: guard against missing JSON body (get_json silent=True, empty-string check)
- app.py: replace infinite redirect with 404 for unknown /api/* and /setup/* paths
- tools/jwtdecoder.py: add algorithms list to jwt.decode() for PyJWT 2.x compatibility
- util/setup_routes.py: call reset_pool() after save_config() so pool re-initialises with new DB credentials
- util/logger.py: set ERROR level on error.log handler so it no longer receives INFO/WARNING messages
- LoginForm.jsx: remove dead navigate() call that was immediately overridden by window.location.href
- main.jsx: remove base.css, dark.css, light.css that were already imported in App.jsx (duplicate imports)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/util/logger.py

@@ -1,19 +1,21 @@
 import logging
 import os
 
-# Ensure logs directory exists
 os.makedirs("logs", exist_ok=True)
 
-# Configure logger
+fmt = "%(asctime)s [%(levelname)s] %(message)s"
+
+error_handler = logging.FileHandler("logs/error.log")
+error_handler.setLevel(logging.ERROR)
+
 logging.basicConfig(
     level=logging.INFO,
-    format="%(asctime)s [%(levelname)s] %(message)s",
+    format=fmt,
     handlers=[
         logging.FileHandler("logs/app.log"),
-        logging.FileHandler("logs/error.log"),
+        error_handler,
         logging.StreamHandler()
     ]
 )
 
-# Hauptlogger, wird von anderen Modulen importiert
 logger = logging.getLogger("main")